This invention generally pertains to a flexible substrate on which a plurality of light sources are mounted, and more specifically, to a plurality of solid-state light sources mounted on a flexible substrate for use in a lamp to provide room illumination.
Incandescent bulbs are one of the least efficient light sources, yet they still comprise a substantial portion of the lighting used in homes and businesses. It has long been recognized that fluorescent lighting and halogen lamps produce light much more efficiently and last substantially longer, yet even in new construction, incandescent bulbs are often used instead of the more efficient alternative types of bulbs. One of the causes delaying the general acceptance and greater use of more efficient lighting has been the initial cost of non-incandescent lighting. Although the total cost of installation and the energy required for operating non-incandescent lighting systems is substantially less than incandescent lighting, the initial cost can be significant and often discourages the installation of alternative lighting fixtures. Moreover, home and business owners are often reluctant to replace an incandescent bulb fixture with a relatively expensive fluorescent lamp and ballast assembly or other alternative lighting fixture.
Recognizing that the cost and difficulty of replacing incandescent lighting fixtures has been a significant deterrent to the acceptance of alternative lighting in new installations and the replacement of incandescent lamps with alternative lighting systems, several different compact fluorescent lamp and ballast assemblies have been developed that include a conventional incandescent lamp threaded base and which are sized to retrofit incandescent lamps in conventional incandescent lamp sockets. By using such retrofit fluorescent lamps, the need to replace the incandescent lamp with a separate ballast and other components of the type normally required for a fluorescent lamp is avoided. Although retrofit fluorescent lamps are substantially more expensive than the incandescent bulbs they replace, the retrofit lamps have a much longer expected life and use much less electrical power to produce a light output equivalent to that of the incandescent bulb that they replace.
Unfortunately, many people are unwilling to pay the cost of a retrofit fluorescent lamp, even though they may recognize that these lamps will provide long-term savings. The problem appears to be that the initial cost of retrofit fluorescent lamps is too high and the non-incandescent lamps, although they may last for several thousand hours, will eventually dim and fail, requiring replacement. What is needed is a different type of alternative lamp for retrofitting incandescent lamps that can be made and marketed at a substantially lower cost than conventional retrofit fluorescent lamps, and which will provide greater efficiency and longer life.
Light emitting diodes (LEDs) have recently been developed that produce white light at a substantially greater intensity than earlier LEDs of this type. In the prior art, U.S. Pat. No. 5,463,280 (Johnson) discloses an LED retrofit lamp for use in replacing incandescent lamps employed in EXIT signs and the like. Instead of requiring up to 20 watts of a conventional incandescent light bulb used in an EXII sign, this retrofit LED lamp produces about the same output level of light, only consumes about two watts of power, and can operate for at least 25 years. As described in this patent, a plurality of LEDs emitting red light (peak wavelength of 650-670 nm) are mounted on elongate printed circuit (PC) boards in a linear, spaced-apart array. The PC boards include conductors that electrically connect the LEDs in series. Two such PC boards are stacked back-to-back and connected to an alternating current (AC) line power source through a current limiting circuit. In one embodiment, the current limiting circuit includes a capacitor connected in series between the AC line and a rectifier. In another embodiment, a resistor is used to limit the current to a rectifier and through the series-connected LEDs. In still another embodiment, a switching power supply provides current to the LEDs. While the invention disclosed in this reference may be suitable for its disclosed intended use, it is not suitable for providing general ambient or task lighting, because the light emitted by the LEDs is red in color and is not uniformly distributed around the elongate glass tube in which the PC boards and current limiting power supply are housed. Instead, the light is concentrated at diametrically opposite sides of the back-to-back PC boards, which is acceptable in an exit sign that is only visible from opposite sides. Also, if any LED should fail in the series-connected string disclosed in this prior art patent by becoming open-circuited, the failure will likely cause the entire string of LEDs to stop producing light. Clearly, this prior art device is not acceptable as a retrofit for incandescent bulbs used for general ambient room and task lighting. A more suitable solution is required if LED light sources are to be usable as replacements for incandescent bulbs in general ambient and task light applications.
In accord with the present invention, a lamp is defined for use in a conventional line current powered incandescent lamp socket, for providing area or task lighting. The lamp includes a base that is adapted to electrically and mechanically engage a conventional lamp socket and thus, to receive an alternating current (AC) via electrical terminals disposed on the base. A power supply is electrically connected to the electrical terminals on the base and receives the AC at a line voltage. The power supply limits a voltage and a magnitude of an electrical current produced at an output of the power supply. A flexible substrate on which a plurality of electrical conductors is disposed is included within the lamp. The flexible substrate is formed to generally define a cylinder that has one end disposed adjacent to the base. The plurality of electrical conductors are electrically connected to the output of the power supply. A plurality of solid-state light sources are mounted on an outer surface of the flexible substrate in a spaced-apart array, so that light emitted by the solid-state light sources when they are electrically energized is distributed radially about an entire circumference of the lamp. Each of the solid-state light sources is electrically connected to the plurality of electrical conductors disposed on the flexible substrate, so that the light sources are energized by the electrical current from the power supply. A generally cylindrical light transmissive envelope having an end attached to the base encloses the flexible substrate and the plurality of solid-state light sources. This light transmissive envelope protects the plurality of solid-state light sources, while transmitting the light that they emit.
Preferably, the plurality of solid-state light sources comprise light emitting diodes that emit a white light, although it is also contemplated that other types of solid-state light sources can instead be used.
The plurality of conductors disposed on the flexible substrate are preferably configured to electrically couple at least a portion of the plurality of solid-state light sources in parallel. In at least one preferred form of the invention, the power supply includes a transformer, and can also include a rectifier. The power supply is preferably disposed inside the base of the lamp.
Either a conductive adhesive or solder can be used to mount the plurality of solid-state light sources on the flexible substrate. In one embodiment, the plurality of solid-state light sources each include at least one terminal that is coupled to at least one of the plurality of conductors on the flexible substrate by a conductive lead.
A cylindrical support is employed for the flexible substrate in one embodiment, and the flexible substrate comprises an elongate thread on which the plurality of solid-state light sources are mounted in a linearly spaced-apart array. The elongate thread is helically wound around an outer surface of the cylindrical support, with the plurality of solid-state light sources disposed so as to emit light radially outward relative to a central axis of the cylindrical support.
For use in retrofitting a conventional three-way light bulb, the base includes three electrical terminals that are adapted to electrically connect with corresponding terminals of a three-way incandescent lamp socket. The three electrical terminals of the base are connected to corresponding different input terminals of the power supply. In this embodiment, the plurality of solid-state light sources are divided into at least two portions, and the power supply responds to application of an AC line voltage to specific input terminals to selectively energize the portions of the plurality of solid-state light sources, thereby varying a light intensity produced by the lamp as a function of the input terminals of the power supply that are energized with the AC line voltage.
The flexible substrate, or cylindrical support, preferably also includes an outer end on which a plurality of the solid-state light sources are also mounted in a spaced-apart array.